[Voice Mail] Minimum Recording time?

Many of my extensions get many empty messasges in the voicemail. it is basically when the user did not answer and the caller hang up. so I hear many times just beep neep beep like 3 times. Its about 3sec.

My question is simple, is it possible that FreePBX will only save messages longer then 3 seconds?

Yes. You change this in Voicemail Admin.